1. Field of the Invention
The present invention relates to a circuit controller for opening and closing a switching circuit that allows or disallows energization with current supplied from a d.c. power source through a limiting resistor. The invention also relates to an inrush current limiting circuit and an inverter that are equipped with such a circuit controller.
2. Description of Related Art
There have been proposed various circuit controllers for opening and closing a switching circuit that allows or disallows energization with current supplied from a d.c. power source through a limiting resistor. Also, various inrush current limiting circuits and inverters, which are each equipped with a circuit controller of the above type, have been proposed. (see e.g., Japanese Patent No. 3289743 and Japanese Patent No. 3269377).
Japanese Patent No. 3289743 discloses a technique according to which a filter circuit, which has the same time constant as the time constant dependent on the electrostatic capacitance of a smoothing capacitor of an inverter and on the resistance value of a limiting resistor of the inverter, is used and the current flowing in the limiting resistor is shut off in accordance with a comparison between the output voltage of the filter circuit and the voltage of the smoothing capacitor. More specifically, if the voltage of the smoothing capacitor is lower than the output voltage of the filter circuit, it is determined that a failure such as short-circuit has occurred in the inverter or the smoothing capacitor and the current flowing in the limiting resistor is shut off.
Japanese Patent No. 3269377 discloses a technique according to which after a specified period of time has elapsed after a start of energization, the voltage of the smoothing capacitor is measured and this measured voltage of the smoothing capacitor is compared to a reference voltage for the smoothing capacitor in a normal condition that has been stored beforehand, to thereby determine whether the current flowing in the limiting resistor is to be shut off. More specifically, if the measured voltage of the smoothing capacitor is lower than the reference voltage, it is determined that a failure such as short-circuit has occurred in the inverter or the smoothing capacitor and the current flowing in the limiting resistor is shut off. Another technique is disclosed in which a temperature sensor (that is a thermistor in the embodiment of this patent) for detecting the temperature of the limiting resistor is provided and a check is made to determine whether the temperature of the limiting resistor detected by this temperature sensor exceeds a specified value. If the temperature exceeds the specified value, the energization is shut off.